A prospective evaluation of therapeutic drug monitoring.

Since therapeutic drug monitoring is rapidly becoming a widely used tool in clinical medicine, we prospectively assessed 390 serum drug assays over a 4-week period to determine the appropriateness of serum sample collection. The results of appropriately collected samples were used to evaluate the ability of the physician to interpret and apply this information. Of the 244 samples evaluated in the study, 104 (43%) were inappropriately collected. The physician apparently misapplied the results in 40 of 101 (40%) instances. When combined, this represented a misuse of therapeutic drug monitoring 70% of the time and documented an unjustifiable expense of $3,600 for the 4 weeks. The magnitude of misuse of this tool warrants the implementation of measures to assure appropriate serum sampling and application of therapeutic drug monitoring.